Statement of Cash Flows Supplemental Data (Details 1) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Supplemental Cash Flow Information
Deferred acquisition fees payable	$ 2,811	$ 7,710
Real Estate Properties [Line Items]
Change in asset retirement obligations	0	3,684	6,842
Distributions payable	51,130	41,712	46,412
Issuance of shares to affiliate in satisfaction of fees due	15,482	15,431
Real estate
Real Estate Properties [Line Items]
Reclassification of assets	26,141	140,141
Operating real estate
Real Estate Properties [Line Items]
Reclassification of assets	(609)	0
Real estate under construction
Real Estate Properties [Line Items]
Reclassification of assets	(38,698)	(140,141)
Accumulated depreciation
Real Estate Properties [Line Items]
Reclassification of assets	1,270	0
Assets held for sale
Real Estate Properties [Line Items]
Reclassification of assets	$ 11,896	$ 0